This study investigated the function of the gravisensing statocyst receptor as a consequence of spaaceflight in the re-adaptation phase after landing. Objectives are to; 1) Determine the regulation of expression of the preproHPep gene (gene that is expressed in the primary statocyst receptor cells) as a consequence of space flight and during the re-adaptation to Earth’s gravity. Regulation of this gene might signal how the statocyst receptor is “tuned” by the gravity vector; 2) Specify the changes in excitability of the gravireceptors of the statocyst organ during the readaptation period following space flight; 3) Investigate the potential changes in intersensory interaction between the photosensory and olfactory pathways and the statocyst receptors; 4) Determine the mechanical and electrical excitability of the statocyst receptor during the readaptation period; and, 5) Measure the changes in the internal Ca2+ concentration in the statocyst receptors in response to mechanical stimulation.
Twenty small (3-8 gm), Helix aspersa, and 15 large (12 -18 gm) snails, Helix lucorum, were flown on Foton-M2. The juvenile snails were divided into two groups for pedal peptide analysis using mRNA expression analysis, and the first half of the samplers were prepared upon receipt of the snails at 30 hours after landing. The other half were processed 12 hours later (2 time periods). The adult snails were weighed, then behavioral tests were conducted to measure their timed negative gravitaxis to tilt. After the behavioral tests and electrophysiological study was conducted to evaluate the intersensory interaction between the photo- and statoreeceptors using natural light and a tilt stimulus in the isolated central nervous system preparation, and an electrophysiology study to evaluate the firing rate modulation of the statorecptor to tilt. Conventional electrophysiological techniques were used.
The behavioral "negative gravitaxis" responses of the snails to a sudden shift in orientation revealed that the flight snails in general responded faster than their control counterparts. The flight snails were faster in their response to pitch stimulation at each phase. These results suggest the existence of changes in the statocyst of the postflight snails.
A change, upregulation, in the expression of a peptide (Pedap peptide) associated with the statocyst was observed. Significant changes were also observed in the intersensory interaction between the photo- and statoreceptors, and orientation selectivity of statocyst responses. The results obtained in this simple animal model open the possibility for identifying other neurobehavioral responses and revealing subcellular processes affected by the space environment.
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